If I had to guess regarding the accessibility of the new Facebook UI, I’d say that an understaffed accessibility team, wanting to do the right thing, got maybe 35% of their suggestions implemented in the initial rollout, with the other 65% punted to somewhere within the next ten major releases, because the powers that be essentially give the FB accessibility team no authority whatsoever, except to trot out their token blind developer(s) to show the corporate “commitment to accessibility”, which they then fail to show at the next sprint planning meeting.
I could be wrong, though.